In literature the systemic toxicity of bupivacaine is widely demonstrated, like the minor toxicity of levobupivacaine and ropivacaine at the same anesthetic potency. The are actually no studies in humans confronting levobupivacaine and ropivacaine under the aspect of efficacy and toxicity.The aim of the study is the assessment of the systemic absorption of local anesthetics during continuous epidural infusion for postoperative pain control.